During the late 1970's and early 1980's, activated carbon-vacuum regeneration hydrocarbon vapor recovery systems were developed to meet the environmental requirements for vapor control at gasoline bulk terminals. These systems were originally designed to meet the clean air standards which were in force at the time. Since that time, the emission standards have become increasingly more strict, leading to the need to develop vapor recovery systems having a greater degree of efficiency. Such systems have generally been relatively complex, have safety problems, and in large measure are relatively difficult to maintain. Specifically,
--U.S. Pat. No. 4,261,716 is directed to an apparatus for recovering hydrocarbons from an air-hydrocarbon vapor mixture including a pair of adsorbers containing beds of adsorbent having first and second connections on opposite sides of the beds, a first conduit means connected to the first connection of the adsorbers for conducting the air-hydrocarbon vapor mixture to the adsorber and for evacuating the adsorbers, a second conduit means connected to the second connection of the adsorbers for conducting residue gas exiting the adsorbers to the atmosphere, a vacuum pump having a suction connection and a discharge connection, a third conduit means connected between the suction connection of the vacuum pump and the first conduit means, an ejector jet pump disposed in the third conduit means, and an absorber. PA1 --U.S. Pat. No. 4,276,058 is directed to a process for recovering hydrocarbons from an inlet air-hydrocarbon vapor mixture which includes the steps of (1) dividing a flow of liquid absorbent having an affinity for hydrocarbons into a first portion and a second portion, (2) passing the first portion of the liquid absorbent in heat exchange relationship with seal liquid used by a vacuum pump so that the seal liquid is cooled and the first portion of the liquid absorbent is heated, and (3), thereafter, contacting the air-hydrocarbon mixture produced in an adsorber with the heated first portion of the liquid absorbent so that a portion of the hydrocarbons are removed therefrom and a residue gas stream comprised of air and a portion of hydrocarbons is produced. PA1 --U.S. Pat. No. 4,331,456 is directed to an improved process for recovering hydrocarbons from an inlet air-hydrocarbon mixture including the steps of evacuating a bed of activated carbon in an adsorber with a liquid seal vacuum pump while further evacuating the bed by an ejector jet pump. PA1 --U.S. Pat. No. 4,338,101 is directed to a process for recovering hydrocarbons from an inlet inert gas-hydrocarbon vapor mixture including the steps of passing a cooling medium through a cooling jacket of a vacuum pump so as to cool the pump and an inert gas-hydrocarbon mixture pumped thereby. PA1 --U.S. Pat. No. 4,343,629 is directed to a process and apparatus for recovering hydrocarbon from an inlet air-hydrocarbon vapor mixture including, inter alia, the cooling of beds of solid adsorbent by flowing a liquid absorbent through heat transfer coils disposed in the beds of solid adsorbent. PA1 --U.S. Pat. No. 4,462,811 is directed to a process for recovering hydrocarbons from an air-hydrocarbon vapor mixture including (1) circulating absorbent liquid through an absorber during cycles of alternately desorbing first and second carbon beds and (2) interrupting the circulation of absorbent periodically during the initial period of desorption of each hydrocarbon bed until the level of hydrocarbon content in the air-hydrocarbon vapor exhausted from each carbon bed is sufficiently high to be at least partially absorbed in the absorber. Additionally, this patent discloses an apparatus for recovering hydrocarbons from an air-hydrocarbon vapor mixture including, inter alia, a control means for interrupting the flow of absorbent liquid periodically in response to the stage of desorption of an adsorber bed. PA1 --U.S. Pat. No. 4,066,423 is directed to a process for recovering light hydrocarbon from an air-hydrocarbon mixture comprising adsorbing hydrocarbon components from an air-hydrocarbon mixture, absorbing substantially all of the adsorbed hydrocarbon components in an absorber operating with a sufficiently high L/V ratio to produce a constant composition absorber overhead gas containing hydrocarbon and a recovered liquid hydrocarbon mixed with the absorbent, cooling a portion of the recovered liquid hydrocarbon and recycling the cooled recovered hydrocarbon liquid for use as liquid hydrocarbon absorbent in the absorption step. PA1 --U.S. Pat. No. 4,305,734 is directed to a process for recovering hydrocarbon components from a hydro-carbon-carrier gas mixture including the steps of (1) flushing an adsorbent material with a flushing stream of gas which will be adsorbed to a greater degree than the carrier gas so as to displace and vent the carrier gas from the adsorber and (2) lowering the pressure of the hydrocarbon laden adsorbent material so as to desorb the hydrocarbon components therefrom and produce a product stream rich in adsorbed hydrocarbon components. PA1 --U.S. Pat. No. 4,670,028 is directed to a process in which hydrocarbon components are removed from an inlet air-hydrocarbon mixture and passed through a liquid hydrocarbon absorbent absorber wherein the improvement comprises producing a flashed absorbent stream by flashing an effective amount of liquid having an affinity to absorb hydrocarbon components from the inlet air-hydrocarbon mixture.
Although each of the above noted patents discloses vapor recovery systems having varying degrees of efficiency, there is a need for a system which is simplified, has a greater degree of safety and is more easily constructed and maintained.